gpsd is a daemon that listens to a GPS or Loran
receiver and translates the positional data into a
simplified format that can be more easily used by
other programs, like chart plotters. The package
comes with a sample client that plots the location
of the currently visible GPS satellites (if
available) and a speedometer. It can also use
DGPS/ip.

GRASS (the Geographic Resources Analysis Support System) is a software raster- and vector-based GIS (Geographic Information System), image processing system, graphics production system, and spatial modeling system. It contains many modules for raster data manipulation, vector data manipulation, rendering images on the monitor or paper, multispectral image geocoding and processing, point data management and general data management. It also has tools for interfacing with digitizers, scanners, and the PostgreSQL, DBF, and ODBC connected databases. GRASS operates on all common operating systems.

Gpsdrive is a map-based navigation system. It displays your position on a
zoomable map provided from a NMEA-capable GPS receiver. The maps are
autoselected for the best resolution, depending of your position, and the
displayed image can be zoomed. Maps can be downloaded from the Internet with
one mouse click. The program provides information about speed, direction,
bearing, arrival time, actual position, and target position. Speech output is
also available.

SaVi is satellite visualization software that lets you create, run, examine, and modify satellite orbits in two and three dimensions. Simulations of Iridium, Globalstar, Galileo, GPS, and other satellite constellations are included. SaVi requires Tcl and Tk on a system with Unix libraries. SaVi works well with the 3D renderer Geomview. Geomview is optional, though recommended for its 3D rendering capabilities.

Quantum GIS (QGIS) is a cross-platform Geographic
Information System (GIS). It offers support for
vector and raster formats, including spatially
enabled tables in PostgreSQL using PostGIS, common
GIS vector formats such as Shapefiles, and
geo-referenced rasters (TIFF, PNG, and GEOTIFF).
Many plugins are available to dynamically add new
functionality. Viewing of GRASS layers (vector and
raster) is provided by a plugin. GRASS vector
layers can be edited in QGIS.

RoadMap is a navigation program for Unix and
PocketPC that displays street maps. Most of the
maps are provided by the US Census Bureau, and
thus only the US has a decent coverage at this
time. A specific area can be displayed by entering
a street address (street number, street name,
city, and state). It interfaces with a GPS
receiver through gpsd or the serial line to track
the car position. It has been designed to be
usable on a Linux desktop or laptop computer, or
on a PDA (Linux or PocketPC).

GPSBabel converts waypoint data between about fifty file formats, including Magellan and Garmin
serial, Garmin USB, Mapsource, Mapsend, Streets & Trips, Delorme, National Geographic, many PDA formats,
and many others. It is endian and word-size safe,
includes a GUI, and runs on a variety of operating
systems. It also supports Groundspeak GPX
extensions for geocaching.

Engauge Digitizer is digitizing software that converts an image showing a graph or map into numbers. The image file can come from a scanner, digital camera, or screenshot. The numbers can be read on the screen, and written or copied to a spreadsheet. Highlights for beginners include an intuitive interface and extensive context-sensitive documentation. Highlights for experts include compensation for image distortion, cartesian and polar coordinates, linear and logarithmic coordinates, automatic scanning, graphical previews, and browser help.